Device for accurately dosing a continuous flow of fine-granular powder

ABSTRACT

A device for accurately dosing at a previously adjustable value a continuous flow of fine-granular powder having a particle size of smaller than approximately 20 microns out of an outlet aperture of a storage container. The container is provided with a sheathlike thin-walled member which is open on its lower side and vibrates approximately parallel to the direction of flow of the powder. The wall of the member is substantially gridlike and the open end of the member is arranged with a small amount of play in the outlet aperture of the container.

United States Patent 8 T N W MA 3 55 CT MA m n D E n N U M U [72] Inventors Peter Theodorus Joeeph Dex;

Willem Lnlten, Emmulngel, Elndhoven, both at Netherlands App]. No. 873,884

222/246 222/366 X 222/409 X 222/409 X [22] Filed Nov.4,l969

[45] Patented Nov.9, 1971 [73] Auignee U.S.Phlllpe Corporation New York, N.Y. Nov. 13, 1968 Netherlands p, Jr.

[32] Priority 311 6,816,124

[54] DEVICE FOR ACCURATELY DOSING A ABSTRACT: A device for accurately dosing at a OUS FLOW 0F FINE'GRANULAR adjustable value a continuous flow of fine 5 Cl I 7 Dnwh a having a particle size of smaller than a microns out of an outlet aperture ofa stora 24, DIG. 40, l0l, 1 12, l 13 aperture of the container.

PATENTEDuuv 91971 3,618,830

sum 1 or 2 28 f l INVENTORI PETER T. J. BEX WILLEM LUITEN BY iswvg K AGEN DEVICE FOR ACCURATELY DOSING A CONTINUOUS FLOW F FINE-GRANULAR POWDER The invention relates to a device for accurately dosing, at apreviously adjustable value, a continuous flow of fine-granular powder, having a particle size of less than approximately microns. Powder having such small dimensions does not flow at an even rate from a small aperture in a container. Forces between the particles (van der Walls forces), form bridges so that the flow of powder becomes nonuniform and is sometimes even interrupted entirely.

When the friction between the particles and the wall of the container is high, said bridges may become stable. In a conical container having two inclined walls, even a smaller wall friction is sufficient to form bridges. It can furthermore be demonstrated that the influence of the surface roughness of the grains on the formation of bridges becomes larger as the grains are smaller.

The device of the invention is characterized in that a sheathlike thin-walled member, which is open on its lower side, is provided in the container and vibrates approximately parallel to the direction of flow of the powder. The wall of said member is substantially grid-shaped and its open end is arranged with a small amount of play in the outlet aperture. As a result of this the formation of bridges is prevented. The powder flows through the gridlike apertures, in a continuous flow into the interior of the sheathlike member and out of said member through the outlet aperture, for example, into an article to be filled.

It would be possible to vary the quantity of powder by adjusting the aperture of the sheath. However, according to an embodiment of the invention, it is simpler and more efficacious to adjust the quantity of powder flowing out of the device by varying the amplitude and/or the frequency of the vibration of the sheathlike member.

The storage container may have various shapes. According to a further embodiment of the invention, the storage container has a rectangular cross section and at least two oppositely located walls enclose an angle with each other and the sheathlike member has a constant rectangular cross section throughout its length, at least the sidewalls of the sheath situated opposite to the inclined walls consisting of grids. This container and the associated member can easily be manufactured.

According to another embodiment of the invention which is sometimes desirable, the storage container has the form of a conical surface and the sheathlike member which is open at least on its lower side, has a constant circular cross section throughout its length, the sheath wall being constructed as a grid.

According to an embodiment of the invention and in order to prevent the formation of bridges in the powder, said sheathlike member comprises radial fins which are likewise constructed as grids.

The said radial fins, according to still a further embodiment o." the invention, may each comprise two oppositely located gridlike plates, the space between the plates communicating with the space inside the sheathlike member.

In order to minimize the frictional resistance between the powder and the inner walls of the container the inner wall may be lined with a material the friction of which with the finegranular powder is small.

Although the vibration of the sheathlike member can be produced in various manners, it is of advantage to produce said vibration pneumatically. In this case it is found that the vibration, as far as the amplitude is concerned, no longer depends upon the level of the powder in the container. Moreover, in this case the control is simple.

In order that the invention may be readily carried into effect, a few examples of the invention will now be described in greater detail, by way of example with reference to the accompanying drawings, in which:

FIG. I diagrammatically shows a bridge which is formed in a rectangular storage container which is partly filled with molybdenum powder having a grain size of from 6 to 8 microns,

FIG. 2 shows the same situation in a storage container having two inclined walls and filled with the same powder,

FIG. 3 is an isometric elevation of a storage container having two walls which enclose an angle with each other and a partly broken-away front wall provided with a vibrating sheathlike member,

FIG. 4 is a cross-sectional view through the sheathlike member shown in FIG. 3,

FIG. 5 diagrammatically shows a conical storage container having a circular sheathlike member with fins,

FIG. 6 is a plan view ofFIG. 5,

FIG. 7 is a plan view of the container shown in FIG. 5, but in this case the sheathlike member has double fins.

Reference numeral 1 in FIG. 1 denotes a small container having a rectangular cross section which is partly filled with a fine-granular powder 2 the grain size of which is approximately from 6 to 8 microns and which is to flow out of the container in an accurately dosed manner. Owing to the friction with the sidewalls denoted by arrows 3, as well as the mutual friction of the grains with each other and the occurring van der Walls forces between the grains, the powder does not flow but forms a bridge 4. When this bridge is interrupted, a quantity of powder will flow but a new bridge will be rapidly formed again. A continuously and accurately dosed flow of powder is consequently not possible. The same is found to be the case when a container 5 (FIG. 2) having two inclined walls is used in which a bridge 6 is formed; the frictional forces against the walls are again denoted by arrows 7.

FIG. 3 shows an embodiment of a dosing device according to the invention, in which molybdenum powder having a grain size of from 6 to 8 microns can flow out of a storage container in an accurately dosed manner and continuously This storage container 10 comprises two parallel walls 11 and I2 and two walls 13 and I4 enclosing an angle with each other, so that a gap-shaped aperture 15 is formed in the lower part of the container. The container comprises a sheath having a rectangular cross section and consisting of two narrow columns 16 and 17 and two walls 18 and 19, see also FIG. 4. In a practical construction of the device these latter walls consist of spring steel having a thickness of 0.15 mm. and provided with rectangular apertures 20, while the ridges between the apertures have a width of 0.8 mm. The whole width of each wall was 70 mm. The columns 16 and 17 are manufactured from the synthetic resin known commercially as Teflon (polytetrafluoroethylene). On its upper side the sheath is closed by a beam 21 manufactured from the same synthetic resin, which beam is provided with a rod 22. Vibration is imparted to the rod, in a known manner, such as pneumatically, in the direction of the arrow 23. This vibration is adjustable with regard to frequency and amplitude. The columns and hence the sheath are guided through guides 24 likewise consisting of polytetrafluoroethylene.

In order to minimize the friction of the powder with the walls, said walls ll, I2, 13, 14 are lined with a synthetic resin, preferably the above-mentioned polytetrafluoroethylene.

As a result of the vibrating movement of the sheathlike member, bridges cannot be formed in the powder and it has been found that a continuous flow of powder flows out of the sheath, the quantity of said flow being dependent upon the frequency and/or amplitude of the vibration given to the member.

It is not necessary for the vibration to be produced pneumatically; it is alternatively possible to produce said vibration by an assembly of a magnet and springs, or differently, but it has been found that the vibration is sometimes also dependent to a slight extent upon the degree of filling the container.

For example, the grid apertures in the grid shown of spring steel having a thickness of 0.15 mm. may be obtained by etching.

FIGS. 5 and 6 show a container 25, the boundary of which is a conical surface, having a cylindrical outlet aperture 26. This container also has a sheathlike member 27 the wall of which is perforated analogous to the manner shown in FIGS. 3 and 4. A vibration in the longitudinal direction of the sheath 27 is given to the shaft 28 secured to the sheath 27. The sheath 27 is moreover provided with perforated fins 29. This embodiment also ensures a continuous, dosed flow of powder. The inner walls of the container may be polished or be provided with a synthetic resin, which has a low friction relative to the powder to be dosed.

The smooth and continuous flow of powder can even better be realized when the perforated fins 29 as shown in FIG. 7 are given a double construction. Perforated fins 30 and 31 each time form one assembly having a small space between the individual fins.

What is claimed is:

l. A device for accurately dosing a continuous flow of finegranular powder having a particle size of less than approximately 20 microns in diameter comprising a storage container, an outlet aperture at the bottom of said container through which said continuous flow of powder is to pass, a sheathlike thin-walled member arranged within said container, said sheathlike member being open at its lower end for communicating with said aperture at the bottom of the container, the walls of said member being grid-shaped and having a plurality of apertures for allowing passage of said powder, the open end of said member being arranged with small amount of play in said outlet aperture container, means for causing vibratory motion at an adjustable frequency and amplitude of said sheathlike member so that as said member is vibrated the granular powder in said container is caused to pass through said aperture at a continuous rate, and means for adjusting the amount of powder to pass at said continuous rate.

2. The device according to claim 1 wherein said storage container has a rectangular cross section and comprises two oppositely located parallel walls and two walls joining said parallel walls enclosing an angle with each other, said aperture at the bottom of said container being located at the apex of said angle, and wherein said sheathlike member has a rectangular cross section throughout its length, the side walls of said member being arranged perpendicular to the parallel walls of the container.

3. The device according to claim 1 wherein the storage container has a circular cross section and a conical outer surface and wherein said sheathlike member has a constant circular cross section throughout its length.

4. The device according to claim 3 wherein the walls of said circular sheathlike member are comprised of radial fins which are likewise constructed as grids.

5. The device according to claim 4 wherein said fins comprise two oppositely located gridlike plates, the space between the plates communicating with the space inside the sheathlike member.

#1 i I i 

1. A device for accurately dosing a continuous flow of finegranular powder having a particle size of less than approximately 20 microns in diameter comprising a storage container, an outlet aperture at the bottom of said container through which said continuous flow of powder is to pass, a sheathlike thin-walled member arranged within said container, said sheathlike member being open at its lower end for communicating with said aperture at the bottom of the container, the walls of said member being grid-shaped and having a plurality of apertures for allowing passage of said powder, the open end of said member being arranged with small amount of play in said outlet aperture container, means for causing vibratory motion at an adjustable frequency and amplitude of said sheathlike member so that as said member is vibrated the granular powder in said container is caused to pass through said aperture at a continuous rate, and means for adjusting the amount of powder to pass at said continuous rate.
 2. The device according to claim 1 wherein said storage container has a rectangular cross section and comprises two oppositely located parallel walls and two walls joining said parallel walls enclosing an angle with each other, said aperture at the bottom of said container being located at the apex of said angle, and wherein said sheathlike member has a rectangular cross section throughout its length, the side walls of said member being arranged perpendicular to the parallel walls of the container.
 3. The device according to claim 1 wherein the storage container has a circular cross section and a conical outer surface and wherein said sheathlike member has a constant circular cross section throughout its length.
 4. The device according to claim 3 wherein the walls of said circular sheathlike member are comPrised of radial fins which are likewise constructed as grids.
 5. The device according to claim 4 wherein said fins comprise two oppositely located gridlike plates, the space between the plates communicating with the space inside the sheathlike member. 